Analysis of dispersion characteristics of shear-horizontal-type surface acoustic waves under waveguide structures

We propose a method of analyzing dispersion characteristics of shear-horizontal (SH)-type surface acoustic waves (SAWs) propagating under waveguide structures. SH-type SAWs on 36-42YX-LiTaO3 have widely been used in RF filters of mobile communication systems, and it has strongly been required to clear up loss mechanisms caused by energy leakage to the transverse direction. In this paper, we adopt the orthorhombic system in the following simplified model; the orthorhombic system possesses the slowness very similar to that of 3642YX-LiTaO3, First, elastic coefficients of the orthorhombic system are estimated so that they give the slowness of SH-type SAWs on 36YX-LiTaO3. Secondly, by applying thus determined elastic coefficients to an SAW waveguide structure, simplified dispersion equations in the transverse direction are derived. Solving them, therefore, one can easily characterize the transverse mode behaviors of SH-type SAWs on 36YX-LiTaO3. The method should be effective in a simple analysis of the dispersion characteristics of SH-type SAWs on 36-42YX-LiTaO3 and improving SH-type SAW filter performances.